Greenhouse heating system

ABSTRACT

A radiant heating system for a greenhouse utilizing radiator tubing formed from substantially gas impermeable plastic material. The system includes a radiator tube disposed overhead and formed from light transmitting material so that sunlight projecting into the greenhouse will be substantially transmitted to the plants grown thereunder and a second radiator tube disposed proximate the greenhouse floor and formed of similar plastic material. The radiated tubes are interconnected at one of their ends and a burner communicates through a manifold connected to the other ends of the radiator tubes to transmit a heated effluent through the tubes. Valve means and exhaust means are associated with the manifold. The valve means operates to selectively direct the heated effluent from the burner to the overhead radiator tube for subsequent movement through the inner connection and the floor radiator and back to the manifold for discharge from the greenhouse through the exhaust means, or to direct the heated effluent from the burner to the floor radiator tube for subsequent movement through the inner connection and the overhead radiator and back to the manifold for discharge from the greenhouse through the exhaust means. This allows for a primary heating radiator and a secondary or residual radiator in the greenhouse.

FIELD OF THE INVENTION

This invention relates to heating systems and, more particularly, toradiant tube heating systems for greenhouses.

BACKGROUND OF THE INVENTION

In order to grow plants in greenhouses, a proper combination of light,heat, and humidity must be maintained. This combination of light, heat,and humidity should be consistent throughout the greenhouse so thatplants grow uniformly regardless of position therein. At times, therequisite light and heat are provided naturally from the sun, whichprojects radiant energy through the elevated window areas of thegreenhouse. However, it is often too cold during the winter to growplants without some source of additional heat, especially in northernclimates.

Heat may be provided by forced air heaters which distribute heated airdirectly into the greenhouse. However, this arrangement is not entirelysatisfactory for many reasons. A forced air system unevenly distributesheated air initially in the greenhouse, and tends to concentrate theheat in the areas around the heated air outlets. Further, much of thehot air is lost through the roof and walls of the greenhouse beforebeing dispersed throughout the greenhouse. As a result, during thewinter days, the temperature in many areas of the greenhouse can be aslow as 50 degrees which results in improper plant development.

Insulating materials have been used on the roof and walls of thegreenhouse to address the previously mentioned heat loss problemsassociated with direct air heating. A system of this type is disclosedin Cary U.S. Pat. No. 4,064,648, and Ward et al U.S. Pat. No. 4,313,650.Such systems typically provide for reflective insulating panels which,at times, may block direct sunlight from entering the greenhouse andproduce unwanted shadows therein. Such systems are also unsatisfactorysince the plants need uniform heat and light for proper growth.

Radiant heating systems have been used to heat greenhouses. Radiantsystems provide an indirect source of heat and are generally capable ofhaving heating elements which can be more precisely positioned within agreenhouse. Radiant heating systems typically employ metallicenergy-emitting tubular conduits mounted overhead in an area to beheated. Such systems further include a burner which fires a heatedeffluent into the conduit, an opaque reflector mounted over the conduit,and an exhaust system to expel the effluent and products of combustionoutside the greenhouse. One such radiant heater system is disclosed inJohnson U.S. Pat. No. 3,399,833.

A characteristic of these radiant heating systems is the wide variancein the amount of thermal energy emitted from the conduit over itsworking length. While the temperature inside the metallic conduitimmediately adjacent the burner may reach levels in excess of 1600° F.,the temperature inside the conduit at the exhaust end, depending onlength, may be as low as 200° F. This results in an uneven emission ofthermal energy over the length of the conduit. Unless the spacing of thetube from the area being heated is varied, there are correspondinglyuneven temperatures in the area being heated by the system. This isespecially true with low overhead mounted (7'-9') systems in high heatloss structures, such as greenhouses.

One attempt to more evenly distribute the thermal energy radiated by themetallic conduit is disclosed in Prince U.S. Pat. No. 4,319,125. Princeemploys a dispersing reflector adjacent to the relatively hot initialportion of the metallic conduit and a parabolic or concentratingreflector adjacent to the colder end portion of the conduit tocompensate for the varying intensity of thermal energy radiated over thelength of the conduit. While the shaped reflector may provide somemeasure of improvement in the distribution of the thermal energythroughout the area serviced by the heater system, the opaque conduitand reflector obstruct sunlight entering the greenhouse and produce ashadow which adversely affects the growth of plants thereunder.

SUMMARY OF THE INVENTION

The present invention provides a radiant heating system of relativelysimple and inexpensive construction which provides controlled anduniform heating of a greenhouse environment.

According to an important feature of the invention, the radiant heatingsystem includes a tubular conduit which extends to an area to be heatedand is formed from a length of gas impermeable plastic tubing. A burnerconnects to one end of the conduit so that the conduit receives theeffluent output from the burner, thereby providing energy which radiatesfrom the conduit. This arrangement provides an inexpensive radiatorheating system which maintains a substantially even temperaturethroughout the length of the conduit.

According to a further feature of the invention, the tubular conduit isarranged overhead and formed from light transmitting material to allowthe sunlight projecting into the greenhouse to pass through the conduitwithout substantially interfering with the transmission of light to theplants grown thereunder. This arrangement maintains a uniform lightenvironment within the greenhouse for consistent plant growth. In thepreferred embodiment, the tubing is formed from nylon reinforcedpolyethylene, or other suitable light transmitting material, so as toallow the use of a readily available inexpensive material for theconduit.

According to a further feature of the invention, the tubing is formedfrom nonrigid plastic material having a normally collapsed configurationand attains an inflated configuration by the action of the heatedeffluent transmitted through the tubing. This arrangement allows thetubing to normally assume a collapsed configuration, to facilitateshipping and storage, and yet allows the tubing to assume an inflatedconfiguration in response to the passage of heated effluenttherethrough.

According to a further feature of the invention, the system furtherincludes a floor radiator formed of a length of substantially gasimpermeable tubing, preferably of plastic although low emission sheetmetal tubing may be used since sunlight is not a factor, communicatingwith the burner and disposed proximate the greenhouse floor and valvemeans operative to selectively direct the heated effluent from theburner to either the overhead radiator tubing or the floor radiatortubing. This arrangement allows the system to selectively provideradiant heat either to the upper regions of the greenhouse or to thefloor regions of the greenhouse.

According to a further feature of the invention, the system furtherincludes exhaust means, the free end of the overhead tubing is connectedto the free end of the floor tubing, and the valve means is selectivelyoperative to direct the heated effluent to the overhead tubing forsubsequent movement through the floor tubing to the exhaust means or todirect the heated effluent to the floor tubing for subsequent movementthrough the overhead tubing to the exhaust means. This arrangementallows the heated effluent to be directed through an enclosed loop andallows selection of the direction of movement of the effluent throughthe loop to the exhaust.

Further, the exhaust means may direct the exhaust effluent either insideor outside of the enclosure depending on the configuration desired. Forexample, in a greenhouse system it is desirable to minimize heat lossand provide CO₂ for plants to use. As such, exhausting the effluentinside the structure aids in both factors. On the other hand, if thesystem were placed in a high human traffic area, the exhaust can bedirected outside to minimize CO₂ buildup.

An additional related concern involves the placement of the inletrelated to the source of heated air effluent for the system. To minimizehumidity in the local environment, all or a portion of the ambient airmay be ingested by the system. It is important in many applications tocontrol the humidity and thus control the condensation within thestructure. By placing the inlet and exhaust outlet either inside oroutside the structure, humidity can be effectively controlled.

In the disclosed embodiment of the invention, the valve means isconnected to the exhaust means and the burner, the valve means has anoverhead outlet and a floor outlet, one end of the tubing of theoverhead radiator is connected to the overhead outlet of the valvemeans, one end of the tubing of the floor radiator is connected to thefloor outlet of the valve means, the valve means is configured toselectively direct the heated effluent from the burner to the overheadoutlet or to the floor outlet and is further configured to allow theexhaust means to communicate with the outlet other than the outletselected to receive the heated effluent from the burner. The systemfurther includes connector means having an overhead port and a floorport with the overhead port of the connector means attached to the freeend of the overhead radiant and the floor port of the connector meansattached to the free end of the tubing of the floor radiator. Thisspecific arrangement provides a simple and effective means fordistributing the heated effluent initially through the overhead radiatorfor subsequent discharge through the floor radiator and exhaust means orto the floor radiator for subsequent discharge through the overheadradiator and the exhaust means.

According to a further feature of the invention, the effluent is heatedto a temperature of approximate 200° F. so that the radiant output ofthe system corresponds to the absorptivity peak of the floor andsurrounding equipment and structures which allows these components toreradiate the radiant energy. This arrangement optimizes the heattransfer efficiency of the system.

According to a further feature of the invention, the system includes amanifold communicating with the burner, the manifold has a plurality ofupper manifold outlets and a plurality of lower manifold outlets, acorresponding plurality of tubular overhead radiators connect to theupper manifold outlets, a corresponding plurality of tubular lowerradiators connect to the lower manifold outlets, and a plurality ofconnector members operate to connect one of the overhead radiators to arespective one of the floor radiators. This arrangement provides aplurality of closed loop systems which may be positioned within theenclosure to uniformly and effectively heat the enclosure.

According to a feature of the invention methodology, a source of heatedair is provided, one end of a normally non-rigid, collapsed tube isconnected to the source of heated air, the tube is positioned within anenclosure to be heated, and heated air is blown from the source throughthe tube to inflate the tube and provide radiant heat to the enclosure.This methodology provides a ready, efficient and inexpensive means ofuniformly heating an enclosure.

According to a further feature of the invention methodology, the step ofproviding a source of heated air comprises providing a burner and ablower, and the blower operates to blow ambient air through the tube inexcess of the amount of air required for complete combustion of the fuelused by the burner so as to regulate the overall temperature of the airblown through the tube. This methodology allows the system to use thenon-rigid type tube operating at a temperature below the melting pointof associated components.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and aspects of the invention will becomeapparent in the detailed description of the invention hereinafter withrespect to the drawings in which:

FIG. 1 is a perspective view of the invention heating system removedfrom any related enclosure;

FIG. 2 is a side view of the invention heating system disposed in agreenhouse;

FIG. 3 is a side view of a valve means and blower assembly used in theinvention heating system;

FIG. 4 is a detailed view of a section of an overhead radiator used inthe invention heating system;

FIG. 5 is a detailed view of a section of a lower radiator used in theinvention heating system; and

FIG. 6 is a side view of an alternate configuration of the inventionheating system disposed in a greenhouse.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides for the heating of a greenhouse 10 in aneasily assembled, substantially uniform, radiant heating system 12 ofrelatively simple and inexpensive construction. The heating system 12 isgenerally composed of a heat generating and distributing assembly 14 anda radiant heating assembly 16. Generally, the heat generating anddistributing assembly 14 produces a heated air effluent which isprojected through the radiant heating assembly 16 to the area to beheated.

With reference to FIGS. 1 and 2, the heat generating and distributingassembly 14 includes a burner/blower unit 20 and a manifold assembly 22.

Burner/Blower unit 20 includes a blower 70 which operates to project aflow of air from inlet 72 past burner 74 and into connector duct 36. Theoutput of the burner/blower unit 20 is distributed through a valveassembly 34 to a manifold assembly 22 which includes an upper,horizontally disposed, air duct arm 24 having a plurality of outlets 26distributed along the length thereof; a lower horizontally disposed airduct arm 28 also having a plurality of outlets 30 distributed along thelength thereof; a valve assembly 34; a vertically extending duct 32connecting the valve assembly to upper and lower arms 24, 28; ahorizontally extending duct 36 connecting the valve assembly 24 toburner/blower unit 20; and an exhaust duct 82 connecting the valveassembly to the exhaust to the exterior of the greenhouse, throughgreenhouse end wall 10A. All of the components of the manifold assembly22 are formed from a metallic material to provide structural strength tothe overall system 12 and withstand any direct heat from theburner/blower unit 20.

Valve assembly 34 includes a substantially cubic housing 75 having aninternal plate 76 pivoted about a horizontal axis 78 between a firstposition 76a and a second position 76b by operation of an external nob80 mounted coaxially on the pivot axis 78. The exhaust duct 82 andconnector duct 36 are connected to opposite side walls of the housingand vertical ducts 32 are connected to the top and bottom walls of thehousing. The external nob 80 is preferably a motorized unit adapted topivot internal plate 76 in a controlled manner without the need forphysical manipulation.

The heat generating and distributing assembly 14 is disposed proximateend wall 10A of the greenhouse 10 by support arms 38 which engagevertical ducts 32 to position the lower air duct arm 28 and outlets 30near the greenhouse floor 40. The dimensions of the manifold assembly 22and, more specifically, the vertical ducts 32 are such that the upperair duct arm 24 and upper outlets 26 are correspondingly positioned atan elevated overhead position above the greenhouse floor 40.

The radiant heating assembly 16 includes a plurality of tubular overheadradiators 40, a corresponding plurality of lower tubular floor radiators42, and a corresponding plurality of connector tubes 14. The connectortubes 44 are vertically oriented proximate the opposite wall 10B of thegreenhouse 10 by additional support arms 38. Each connector tube 44 hasan overhead port 48 and lower floor port 50. When the connector tubes 44are attached to the opposite greenhouse wall the lower floor port 50 ispositioned proximate the floor 40 and the upper port 48 is positioned atan elevated overhead position. Each overhead radiator 40 connects at oneend to an upper outlet 26 by operation of a clamp 46 which secures theend of the radiator 40 against the outside of the outlet 26 insertedtherein. The other end of each overhead radiator 40 attaches in likefashion to an upper connector port 48 using a clamp 46. Similarly, eachlower tubular floor radiator 42 connects at one end to a lower outlet 30of the manifold assembly 22 and at the other end to the floor port 50 ofa connector tube 44. The radiant heating section 16 is thereby arrangedas a sequence of closed loops formed by related overhead radiators 40,floor radiators 42 and connector tubes 44, which can be positioned inareas of the greenhouse to be heated. Typically, each closed loop ofradiators 40, 42 would be positioned to extend above and below a seriesof one or more tables 60 in the greenhouse 10.

With reference also to FIGS. 4 and 5, each of the tubular radiators 40,42, are configured as energy-emitting conduits formed from a length ofnon-rigid, polyethylene tubing having a diameter in the range of 8 to 20inches to provide substantially gas impermeable plastic radiators 40,42. The non-rigid polyethylene tubing has a relatively thin wallthickness so as to have a substantially collapsed normal configuration40A, 42A which attains an inflated configuration 40B, 42B, by action ofthe heated air effluent transmitted therethrough.

Further, the non-rigid, polyethylene tubing is substantially transparentso as to transmit light projected therethrough. The large diameter ofthe radiators 40, 42 provides sufficient surface area directed towardthe area to be heated so as not to require an opaque reflector. By thisconstruction, the radiators 40 allow sunlight projecting through thegreenhouse window areas to be substantially transmitted through thetubing so as not to interfere with the transmission of light to theplants grown thereunder.

The overhead radiators 40 are suspended from ceiling braces 56 of thegreenhouse 10 by hanging flexible plastic bands 58 which support thetubing at intervals along the length of a given overhead radiator 40.The plastic bands 58 are supported by the braces 56 and provide anon-invasive support for the overhead radiator 40 to maintain theintegrity of the gas impermeable tubing. Further, the bands 58 are alsosubstantially transparent so that they do not block sunlight.

The lower radiators are similarly suspended below greenhouse tables 60by hanging strips 62. The tables 60 support the plants in the greenhouse10, and provide a convenient framework for mounting hanging strips 62which position the lower radiators 42 in proximity to the plants grownthereon.

With reference also to FIG. 3, since the polyethylene has a low meltingpoint, the burner/blower unit 20 operates to produce a low grade heatedair effluent of a temperature below the melting point of thepolyethylene. Blower 70 operates to project an amount of airapproximately 500% in excess of the amount required for the combustionprocesses of the burner 74. While the burner 74 may produce outputtemperatures considerably higher than the melting point of thepolyethylene, the overall heated air effluent produced by theburner/blower unit 20 has a temperature below the melting point of thepolyethylene as a result of the combination of the burner output and theexcess ambient-temperature air.

Preferably, the resulting heated air effluent temperature isapproximately 200° F. For example, a propane burner output of 1000 Bturequires approximately 10 cubic feet of air for complete combustion, andan additional 50 cubic feet of ambient air (or 500% excess air) willcool the overall temperature of the resulting effluent to approximately200° F. Several external factors will vary this relationship, includingthe type of fuel burned and the temperature of the ambient air. However,this approximate relationship remains.

When plate 76 is positioned in first position 76A a flow of effluentoccurs from the blower 70 through the manifold assembly 22 to theoverhead radiators 40, through the connector ducts 36 and lowerradiators 42 back to the manifold assembly 22, and out the exhaust duct82 (as shown by solid arrow 84). When the plate 76 occupies the secondposition 76B the path is substantially reversed and a flow of effluentoccurs from the blower 70 through the manifold assembly 22 to the lowerradiators 42, through the connector ducts 36 and overhead radiators 40back to the manifold assembly 22, and out the exhaust duct 82 (as shownby the dashed arrows 86). This allows the operator of the greenhouse tochoose the radiator 40, 42 which will receive heated air effluent firstand therefore act as the primary radiant heat source (the overheadradiator 40 in position 76A, or the floor radiator 42 in position 76B).The greenhouse will further receive secondary, or residual, heating fromthe radiator 40, 42 which operates later in sequence.

Thus, the radiant heating system 12 provides for selective heating ofthe greenhouse 10. When the effluent is directed first to the lowerfloor radiators 42, the radiant heat is directed at the root zone ofsoil in containers placed on the tables 60. This type of heating is mostappropriate for seedling operations where soil temperature is mostcritical. When the effluent is directed first to the overhead radiators40, the radiant heat is directed at the plant canopy above the tables60. This type of heating is most appropriate for more advanced plantgrowth where environment temperature is most critical.

The low grade 200° F. effluent temperature allows for primary radiatorlengths of over 100 feet without substantial loss of effluenttemperature over that length. Sufficient heat energy is radiated by alarge volume of heated air effluent projected through the tubing and thelarge surface area of the polyethylene tubing. Further, since theeffluent is heated to a temperature of approximately 200° F., theradiant output of the system further corresponds to the absorptivitypeak of the floor and allows the floor to reradiate the radiant outputof the lower radiators 42.

Preferably, the radiator tubing has a diameter greater than 8 inches,and within the range of 12 to 18 inches to closely match the outletdiameter on the typical burner manifold assembly and to providesufficient surface area for heating the greenhouse with a convenientnumber of radiators 40 and 42. However, radiators of various diametersmay be used to accommodate different heating configurations and specificheating needs. For example, in high heat loss situations, a large numberof small diameter (approximately 4 inch) radiators may be disposedthroughout a greenhouse to provide increased radiator surface area forheat transfer so as to more evenly distribute heat therein. Conversely,in low heat loss situations, fewer radiators of possibly larger diameter(up to 36 inches) may be utilized to maintain a minimum amount ofradiator surface area for heat transfer. In either case, the apparatusis configured to allow for relatively complete radiant transfer of heatenergy to the greenhouse such that the exhaust temperature of theeffluent is within approximately 20 degrees or less of the ambientgreenhouse temperature so as to be as thermally efficient as practical.Thus, the exact number, diameter, and lengths of the radiators dependsupon the specific greenhouse parameters, such as heat loss, size, etc.,for the given application.

Further, the exhaust means may direct the exhaust effluent either insideor outside of the enclosure depending on the configuration desired. Forexample, in a greenhouse system it is desirable to minimize heat lossand provide CO₂ for plants to use. As such, exhausting the effluentinside the structure aids in both factors. On the other hand, if thesystem were placed in a high human traffic area, the exhaust can bedirected outside to minimize CO₂ buildup. Thus, by way of example, inFIG. 2, the exhaust duct 82 terminates outside the enclosure 10 so as toexhaust effluent and products of combustion outside of the enclosure 10,while, in FIG. 6, an alternative construction disposes the end ofexhaust duct 82 inside the enclosure 10 to minimize heat loss andprovide CO₂ for plants to use.

An additional related concern involves the placement of the inletrelated to the source of heated air effluent for the system. To minimizehumidity in the local environment, all or a portion of the ambient airmay be ingested by the system. It is important in many applications tocontrol the humidity and thus control the condensation within thestructure. By placing the inlet and exhaust outlet either inside oroutside the structure, humidity can be effectively controlled. Thus, byway of example, the burner/blower unit 20 may be located inside theenclosure 10 (FIG. 2) or outside the enclosure 10 (FIG. 6) depending onthe humidity needs of the structure. It should be noted, that the samefunction can occur by placing the inlet to the burner/blower unit 20 ata specific location without moving the entire burner/blower unit betweenthe interior and exterior of the structure.

In further alternative embodiments, the greenhouse itself may be atemporary structure, such as a light transmissive tent adapted to berelocatably placed in various areas to protect outdoor plants fromexternal elements, such as frost. In other applications, the enclosuresheated with the present system may include other enclosures where theradiators may be exposed to the interior of the building, for exampleopen-area warehouses, garages, or malls.

From the foregoing description of the preferred embodiment it can beseen that various alternative embodiments of the invention can beanticipated without departure from the scope of the invention as definedin the following claims.

We now claim:
 1. A radiant heating system including a burner and atubular energy-emitting conduit extending through an area to be heatedand connected at one end thereof to the burner to receive the burneroutput, characterized in that the conduit comprises a length of tubingformed from a gas impermeable plastic material.
 2. A radiant heatingsystem for an enclosure having a burner arranged to transmit a heatedeffluent through an overhead radiator to heat an area of the greenhousein proximity to the radiator, characterized in that the overheadradiator is formed from a length of light transmitting tubing whichallows sunlight projecting into the greenhouse to be substantiallytransmitted therethrough.
 3. The system of claim 2, whereinsaid tubingis formed from a substantially gas impermeable plastic material.
 4. Thesystem of claim 3, whereinsaid tubing is formed from polyethylene. 5.The system of claim 3, whereinsaid tubing is formed from non-rigidplastic material having a normally collapsed configuration and attainsan inflated configuration by the action of the heated effluenttransmitted therethrough.
 6. The system of claim 3, wherein the systemfurther includes:a floor radiator formed of a length of substantiallygas impermeable tubing communicating with the burner and disposedproximate to the enclosure floor.
 7. The system of claim 6, whereinsaidfloor radiator is formed from a plastic material.
 8. The system of claim6, whereinsaid overhead radiator and said floor radiator are formed fromidentical materials.
 9. The system of claim 6, whereinsaid systemfurther includes valve means operative to selectively direct the heatedeffluent from the burner to one end of the overhead radiator tubing orto one end of the floor radiator tubing.
 10. The system of claim 9,whereinsaid system further includes exhaust means; the other end of saidoverhead tubing is connected to the other end of said floor tubing; andsaid valve means is selectively operative to direct the heated effluentto the overhead tubing for subsequent movement through the floor tubingto the exhaust means or to direct the heated effluent to the floortubing for subsequent movement through the overhead tubing to theexhaust means.
 11. The system of claim 10, whereinsaid valve means isconnected to said exhaust means and said burner, said valve means has anoverhead outlet and a floor outlet, said one end of said tubing of saidoverhead radiator is connected to said overhead outlet, and one end ofsaid tubing of said floor radiator is connected to said floor outlet,said valve means is configured to selectively direct the heated effluentfrom the burner to said overhead outlet or to said floor outlet, andfurther is configured to allow said exhaust means to communicate withthe outlet other than the outlet selected to receive the heated effluentfrom the burner; and said system further includes connector means havingan overhead port and a floor port, said overhead port of said connectormeans being attached to the other end of said tubing of said overheadradiator, and said floor port of said connector means being attached tothe other end of said tubing of said floor radiator.
 12. The system ofclaim 2, whereinsaid light transmitting tubing is substantiallytransparent.
 13. The system of claim 2, whereinsaid light transmittingtubing has a diameter of at least eight inches.
 14. A radiant heatingsystem for an enclosure including a burner, an elongated radiatorconnected at one end thereof to the burner to receive the burnereffluent, and exhaust means at the other end of the radiator todischarge the burner effluent, characterized in that the radiatorcomprises a length of tubing formed from a substantially gas impermeableplastic material.
 15. The system of claim 14, whereinsaid radiator isdisposed overhead; said enclosure comprises a building having elevatedwindow areas; and said substantially gas impermeable plastic material issubstantially transparent to allow sunlight projecting through saidwindow areas to be substantially transmitted therethrough.
 16. Thesystem of claim 14, whereinsaid tubing is formed from non-rigid plasticmaterial having a normally collapsed configuration and attains aninflated configuration by the action of the heated effluent transmittedtherethrough.
 17. The system of claim 14, wherein the enclosure is agreenhouse, further characterized in that:said radiator is disposedproximate to the floor; and said effluent is heated to a temperature ofapproximately 200° F. so that the radiant output of the systemcorresponds to the absorptivity peak of the floor and allows the floorto reradiate the radiant output of the radiator.
 18. The system of claim17, whereinsaid system further includes a second radiator communicatingwith the burner to allow heated effluent to be transmitted therethrough,said second radiator being disposed overhead and formed from a length ofsubstantially transparent tubing to allow sunlight projecting into thegreenhouse to be substantially transmitted therethrough.
 19. The systemof claim 18, whereinsaid system further includes valve means operativeto selectively direct the heated effluent from the burner to one end ofthe overhead radiator tubing or to one end of the floor radiator tubing.20. The system of claim 19, whereinsaid system further includes exhaustmeans; the other end of said overhead tubing is connected to the otherend of said floor tubing; and said valve means is selectively operativeto direct the heated effluent to the overhead tubing for subsequentmovement through the floor tubing to the exhaust means or to direct theheated effluent to the floor tubing for subsequent movement through theoverhead tubing to the exhaust means.
 21. The system of claim 20,whereinsaid valve means is connected to said exhaust means and saidburner, said value means has an overhead outlet and a floor outlet, saidone end of said tubing of said overhead radiator is connected to saidoverhead outlet, and said one end of said tubing of said floor radiatoris connected to said floor outlet, said valve means is configured toselectively direct the heated effluent from the burner to said overheadoutlet or to said floor outlet, and further is configured to allow saidexhaust means to communicate with the outlet other than the outletselected to receive the heated effluent from the burner; and said systemfurther includes connector means having an overhead port and a floorport, said overhead port of said connector means being attached to theother end of said tubing of said overhead radiator, and said floor portof said connector means being attached to the other end of said tubingof said floor radiator.
 22. The system of claim 14, whereinsaid exhaustmeans is adapted to discharge at least a portion of the burner effluentoutside of the enclosure.
 23. The system of claim 14, whereinsaidexhaust means is adapted to discharge at least a portion of the burnereffluent inside said enclosure.
 24. The system of claim 14, whereinsaidburner is configured to receive air from inside the enclosure.
 25. Thesystem of claim 14, whereinsaid burner is configured to receive air fromoutside the enclosure.
 26. A radiant heating system for use ingreenhouses, comprising:a blower unit; a burner arranged to heat the airfrom said blower unit; a manifold communicating with said burner andsaid blower unit and having an upper manifold outlet and a lowermanifold outlet; valve means associated with said manifold toselectively direct heated air to said upper manifold outlet or saidlower manifold outlet; a tubular overhead radiator having first andsecond ends, said first end communicatively attached to said uppermanifold outlet so that heated air may be transmitted therethrough, saidoverhead radiator being disposed substantially above the floor of thegreenhouse and formed from an elongated length of non-rigidsubstantially transparent gas impermeable plastic tubing which allowssunlight projecting into the greenhouse to be substantially transmittedtherethrough, said tubing having a normally collapsed configuration andattaining an inflated configuration by the action of the heated airtransmitted therethrough; a tubular lower radiator having first andsecond ends, said first end communicatively attached to said lowermanifold outlet so that heated air may be transmitted therethrough, saidlower radiator being disposed proximate to the floor of the greenhouse;and an exhaust system communicatively attaching to said second ends ofsaid overhead and said lower radiators to discharge the heated air. 27.The system of claim 26, whereinsaid lower radiator is formed from anelongated length of non-rigid substantially gas impermeable plastictubing which allows the floor to reradiate the radiant output of theradiator, said tubing having a normally collapsed configuration andattaining an inflated configuration by the action of the heated airtransmitted therethrough.
 28. The system of claim 26, whereinsaidoverhead radiator is formed of polyethylene.
 29. The system of claim 27,whereinsaid lower radiator is formed of polyethylene.
 30. The system ofclaim 26, whereinsaid burner is operative to heat the air to apredetermined temperature not exceeding the melting point of theradiator material.
 31. The system of claim 26, whereinsaid systemfurther including connector means having an overhead port and a lowerport, said overhead port of said connector means being attached to saidsecond end of said overhead radiator, and said lower port of saidconnector means being attached to said second end of said lowerradiator; said valve means is connected to an exhaust outlet; and saidvalve means is operative to initially direct the heated air from theburner to either said overhead outlet or to said lower outlet, and isfurther operative to allow said exhaust outlet to communicate with theoutlet other than the outlet selected to initially receive the heatedair from the burner.
 32. The system of claim 31, whereinsaid manifoldhas a plurality of upper manifold outlets and a plurality of lowermanifold outlets; a corresponding plurality of tubular overheadradiators connect to said upper manifold outlets; a correspondingplurality of tubular lower radiators connect to said lower manifoldoutlets; and a plurality of connector means operate to connect one ofsaid overhead radiators to a respective one of said floor radiators. 33.A radiant heating system for an enclosure, comprising:a blower unit; aburner arranged to heat the air from said blower unit to a predeterminedtemperature; a manifold communicating with said burner and blower unitand having an upper manifold outlet and a lower manifold outlet; antubular overhead radiator having first and second ends, said first endcommunicatively attached to said upper manifold outlet so that heatedair may be transmitted therethrough; a tubular lower radiator havingfirst and second ends, said first end communicatively attached to saidlower manifold outlet so that heated air may be transmittedtherethrough, the second end of said lower radiator connected to thesecond end of said overhead radiator; an exhaust system arranged toexpel the heated air from the system; and valve means selectivelyoperative to direct the heated air to the overhead radiator forsubsequent movement through the lower radiator to the exhaust system orto direct the heated air to the lower radiator for subsequent movementthrough the overhead radiator to the exhaust system.
 34. The system ofclaim 33, whereinsaid exhaust system is adapted to discharge at least aportion of the heated air outside the enclosure.
 35. The system of claim33, whereinsaid exhaust system is adapted to discharge at least aportion of the heated air inside the enclosure.
 36. The system of claim33, whereinsaid blower unit is adapted to receive air from outside ofsaid enclosure.
 37. The system of claim 33, whereinsaid blower unit isadapted to receive air from inside of said enclosure.
 38. A radiantheating system for an enclosure, comprising:a blower unit; a burnerarranged to heat the air from said blower unit to a predeterminedtemperature; a manifold communicating with said burner and blower unitand having an upper manifold outlet, a lower manifold outlet, and anexhaust outlet; a tubular overhead radiator having first and secondends, said first end communicatively attached to said upper manifoldoutlet so that heated air may be transmitted therethrough; a tubularlower radiator having first and second ends, said first endcommunicatively attached to said lower manifold outlet so that heatedair may be transmitted therethrough; connector means having an overheadport and a lower port, said overhead port communicatively attached tosaid second end of said overhead radiator, and said lower portcommunicatively attached to said second end of said lower radiator; anexhaust system attached to the exhaust outlet of said manifold arrangedto expel the heated air apart from the system; and valve meansassociated with said manifold operative to selectively direct the heatedair from the burner initially to said overhead outlet or to said loweroutlet, and further being operative to allow said exhaust outlet tocommunicate with the outlet other than the outlet selected to initiallyreceive the heated air from the burner.
 39. The system of claim 38,whereinsaid overhead radiator is formed from a length of lighttransmitting tubing which allows sunlight projecting into the enclosureto be substantially transmitted therethrough.
 40. The system of claim39, whereinsaid light transmitting tubing is substantially transparent.41. The system of claim 40, whereinthe radiator comprises a length oftubing formed from a substantially gas impermeable plastic material. 42.The system of claim 38, whereinsaid lower radiator comprises a length oftubing formed from a substantially gas impermeable plastic material. 43.The system of claim 38, whereinsaid manifold has a plurality of uppermanifold outlets and a plurality of lower manifold outlets; acorresponding plurality of tubular overhead radiators connect to saidupper manifold outlets; a corresponding plurality of tubular lowerradiators connect to said lower manifold outlets; and a plurality ofconnector means operate to connect one of said overhead radiators to arespective one of said floor radiators.